Systems Research and Architecture Group (SRA)
Our Research and Teaching activities are centered around the architecture of computing systems: From hardware over system software up to languages and compilers with a focus on constructive methods for the design and development of adaptable and versatile system software. The group is led by Prof. Daniel Lohmann.
EmbeddedThose machines that are closest to our everyday life are special-purpose systems embedded into the physical world. Due to this embedding, we know a lot about the surroundings of a system. We exploit this knowledge in the design of hardware and system software.
TailoredThe requirements for every system are special. However, we often favor unspecific general-purpose components over special-purpose solutions. With the techniques of automatic tailoring, we can achieve specialized systems at moderate development costs.
SystemsDuring the architectural design, the required functionalities are often well understood. Nonfunctional aspects are decisive for choosing a system for a given task. Especially for embedded systems, we can optimize various aspects towards the given application scenario.
And now for something completely different: Our paper A Bibliometric Approach for Detecting the Gender Gap in Computer Science has appeared on the May 2020 issue of CACM, together with a short video about this work produced by ACM. In the paper we describe a method to identify the ratio of active female CS scientists by bibliometric analyses. In contrast to previous studies in the STEM fields that refer to limited data records (such as enrollment and degree numbers) our method identifes active researchers from all career levels and instutitions and can easily be tailored to specific sub-fields of the STEM field. The percentage of women contributing to 19 representative conferences in systems-level CS within the last six years is, on average, below ten percent.
Oskar Pusz presents our paper Program-Structure–Guided Approximation of Large Fault Spaces at the 24th IEEE Pacific Rim International Symposium on Dependable Computing (PRDC '19) in Kyoto, Japan. In the paper we describe an approach to reduce the number of required fault injections using program-structure informations while aiming full fault-space coverage. Results show that injections can be reduced by up to 76 percent with an deviation of less than 2.7 percent and we keep the locality of the results regarding silent data corruptions to a low deviation.
Tobias Landsberg receives the award for best master thesis in the field of operating systems. The award is granted annually by the SIG on Operating Systems of the German Computer Assiciation (GI Fachgruppe Betriebssysteme) solely on the base of scientific excellence. It includes a price money of 500 €. Congrats, Tobias!
In his thesis Analyzing and Optimizing TLB-Induced Thread Migration Costs on Linux/ARM Tobias evaluates if it is feasable and benefitial to pre-warm the TLB (Translation Look-Aside Buffer) when a thread is migrated to another core. He analyzes existing ARM cores, presents and evaluates possible hardware extensions in gem5 and and provides a complete Linux integration for the system.
Linux Weekly News (LWN) features our recent work on analyzing kernel e-mail and the PaStA tool presented in our ICSE '19 and OpenSym '16 papers and recent talks by Ralf Ramsauer, Sebastian Duda, and Wolfgang Mauerer at ELCE '19 and LPC '19.
PaStA quantitatively analyses the evolution of patch stacks by mining git repositories, which is an important building block for analyzing patch-level optional features in the CADOS project.
Abstract: Mechanical and electronic automation was a key component of the technological advances in the last two hundred years. With the use of special-purpose machines, manual labor was replaced by mechanical motion, leaving workers with the operation of these machines, before also this task was conquered by embedded control systems. With the advances of general-purpose computing, the development of these control systems shifted more and more from a problem-specific one to a one-size-fits-all mentality as the trade-off between per-instance overheads and development costs was in favor of flexible and reusable implementations. However, with a scaling factor of thousands, if not millions, of deployed devices, overheads and inefficiencies accumulate; calling for a higher degree of specialization.
For the area of real-time operating systems, which form the base layer for many of these computerized control systems, we deploy way more flexibility than what is actually required for the applications that run on top of it. Since only the solution, but not the problem, became less specific to the control problem at hand, we have the chance to cut away inefficiencies, improve on system-analyses results, and optimize the resource consumption. However, such a tailoring will only be favorable if it can be performed without much developer interaction and in an automated fashion. Here, real-time systems are a good starting point, since we already have to have a large degree of static knowledge in order to guarantee their timeliness. Until now, this static nature is not exploited to its full extent and optimization potentials are left unused.
The requirements of a system, with regard to the RTOS, manifest in the interactions between the application and the kernel. Threads request resources from the RTOS, which in return determines and enforces a scheduling order that will ensure the timely completion of all necessary computations. Since the RTOS runs only in the exception, its reaction to requests from the application (or from the environment) is its defining feature.
In this thesis, I will grasp these interactions, and thereby the required RTOS semantic, in a control-flow--sensitive fashion. Extracted automatically, this knowledge about the reciprocal influence allows me to fit the implementation of a system closer to its actual requirements. The result is a system that is not only in its usage a special-purpose system, but also in its implementation and in its provided guarantees.
In the development of my approach, it became clear that the focus on these interactions is not only highly fruitful for the optimization of a system, but also for its end-to-end analysis. Therefore, this thesis does not only provide methods to reduce the kernel-execution overhead and a system's memory consumption, but it also includes methods to calculate tighter response-time bounds and to give guarantees about the correct behavior of the kernel. All these contributions are enabled by my proposed interaction-aware methodology that takes the whole system, RTOS and application, into account.
With this thesis, I show that a control-flow--sensitive whole-system view on the interactions is feasible and highly rewarding. With this approach, we can overcome many inefficiencies that arise from analyses that have an isolating focus on individual system components. Furthermore, the interaction-aware methods keep close to the actual implementation, and therefore are able to consider the behavioral patterns of the finally deployed real-time computing system.
Florian Rommel presents our paper Wait-Free Code Patching of Multi-Threaded Processes at the 10th Workshop on Programming Languages and Operating Systems (PLOS '19) co-located with SOSP in Huntsville, Canada. The paper describes an approach to apply run-time code modification in multi-threaded processes without the need to stop all threads on a global barrier. This is achieved by first preparing a patched clone of the process’s address space and then migrating individual threads at predefined quiescence points while all other threads make uninterrupted progress.
Andreas Ziegler presents our paper Honey, I Shrunk the ELFs: Lightweight Binary Tailoring of Shared Libraries at the International Conference on Embedded Software (EMSOFT '19), in New York. In the paper we describe an approach to automatially reduce the footprint of existing shared libraries by removing unneeded functionality with lightweight binary tailoring. Our approach does not require access to the source code and effectively reduces the amount of code in all shared libraries on a Linux-based system by 63 percent and shrinks their files by 17 percent. The reduction in size is beneficial to cut down costs (e.g., lower storage and memory footprint) and eases code analyses that are necessary for code audits.
Lightweight application-specific tailoring of libraries is an important building block in our attempts towards a fully automatic whole-system tailoring of Linux-based infrastructure software in the CADOS project.
Abstract: In der heutigen Wissenschaft und Wirtschaft haben wir es oft mit Systemen zu tun, welche aus Problemen bestehen, die sehr komplex und nicht einfach zu lösen sind. Aufgrund der zunehmenden Komplexität und der teilweise fehlenden Informationen ist es bereits heutzutage nicht mehr möglich, solche Probleme – welche als Blackbox-Probleme klassifiziert werden – per Hand zu lösen. Um das Maximum oder Minimum zu finden, wird auf Optimierungsmethoden zurückgegriffen, die uns ermöglichen, eine optimale Lösung für das Problem zu suchen und ggf. zu finden. Stochastische Methoden haben die letzten Jahre gezeigt, dass sie sehr gut geeignet sind, solche Probleme zu lösen. Der Vorteil der Verwendung von stochastischen Methoden ist, dass sie nicht den Gradienten des zu optimierenden Problems verwenden, so dass sie sowohl bei großen als auch bei komplexen Optimierungsproblemen erfolgreich angewendet werden können. Diese Vielseitigkeit hat aber ihren Preis. Es gibt hauptsächlich drei wesentliche Aspekte, die die Effizienz der Lösung beeinträchtigen:
- Die realen Probleme werden immer größer und komplizierter oder sie müssen in sehr kurzer Zeit gelöst werden, was erhebliche Ressourcen in Zeit und Hardware erfordert.
- Optimierungsprobleme sind durch mehrere lokale Optima charakterisiert, die ein Verfahren zur Vermeidung einer zu frühen Konvergenz erfordern.
- Algorithmen erfordern einige problembedingte Anpassungen ihrer Verhaltensparameter, um bessere Ergebnisse zu erzielen.
Untersuchungen in dieser Arbeit haben gezeigt, dass die Anpassungen zu besse ren Ergebnissen führen. Durch die adaptive Natur des Frameworks, ist es in vielen Rechnerarchitekturen nutzbar und für viele Probleme anwendbar.